It wasn't Kool-Aid. Flavor-Aid is the real culprit.

The phrase "drinking the Kool-Aid" refers to the 1978 Jonestown massacre, in which more than 900 people committed mass suicide by drinking a flavored drink mixed with Valium, chloral hydrate, cyanide, and Phenergan. Kool-Aid's association with Jonestown has turned into a common meme and saying:

With the evidence so clear, why did the phrase "drinking the Kool-Aid" emerge? Mental Floss suggests Kool-Aid's role as being a genericized name for all flavored drinks, the popularity of The Electric Kool-Aid Acid Test, and other factors made it easier to remember "Kool-Aid" than "Flavor Aid."

Why it's worth correcting the Kool-Aid mistake

Many of the strongest arguments to abandon the phrase come from San Diego State University's Jonestown Institute, including: